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MM: Fachverband Metall- und Materialphysik

MM 34: Liquid and Amorphous Metals I

MM 34.5: Vortrag

Mittwoch, 25. März 2009, 15:45–16:00, IFW D

The hydrodynamic limit in liquid titanium: At which length and time scales is it valid? — •Jürgen Horbach and Andreas Meyer — Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 51170 Köln

A combination of neutron scattering experiments and molecular dynamics (MD) computer simulations is used to analyze the dynamic structure factor of liquid titanium near its melting temperature. First, we show that the simulation is in good agreement with neutron scattering, regarding the self part of the dynamic structure factor, S_s(q,ω) (with q the wavenumber and ω the frequency). For both methods, we find that the width of the quasielastic line shows a hydrodynamic q² dependence for wavenumbers up to about 1.0 Å⁻¹, and thus the self-diffusion constant can be extracted in this q range. Second, MD simulations allow for an accurate calculation of the total dynamic structure factor, S(q,ω), over the full relevant range of q and ω. The latter function is compared to the analytically known hydrodynamic prediction that requires the shear and bulk viscosities as well as the thermal diffusion coefficient as an input. The latter transport coefficients are directly computed from the MD simulation. The comparison of the hydrodynamic S(q,ω) with the “exact one” allows for a quantitative determination of the q-ω range where hydrodynamics is valid.